1. Field of the Invention
The present invention relates to a sheet convey apparatus for conveying a sheet as a recording material in a recording apparatus (printer) as an information output device for a computer and the like, or in an image forming apparatus such as a copying machine, a facsimile machine and the like.
2. Related Background Art
In conventional sheet convey apparatuses having a mechanism for conveying a sheet as a recording material picked up by a sheet supply roller to a convey roller and used with recording apparatuses, there was the following method for transmitting a driving force to the sheet supply roller. Such method will now be explained with reference to FIGS. 14 to 17. FIG. 14 is a sectional view of a sheet supply portion of a conventional recording apparatus, and FIGS. 15 to 17 are views showing a driving force transmitting mechanism for the recording apparatus.
In FIG. 14, the recording apparatus comprises a convey roller 1, a pinch roller 2 urged against the convey roller 1 to generate a conveying force, a pinch roller holder 3 mounted for pivotal movement around an axis (not shown) and adapted to hold the pinch roller 2, a pinch roller spring 4 for biasing the pinch roller holder 3 to urge the pinch roller against the convey roller, a sheet supply roller 5 having a sheet supply roller shaft 6, an idle roller 7 rotatably mounted on the sheet supply roller shaft 6, a friction piece 8 urged against the sheet supply roller and the idle roller to separate sheets (recording materials) 12, a friction piece spring 9 for urging the friction piece against the rollers, a pressure plate 10 on which the sheets are stacked and which serves to urge the sheet stack against the sheet supply roller upon supply of sheet, and a pressure plate spring 11 for biasing the pressure plate toward the sheet supply roller.
FIG. 15 shows a driving force transmitting mechanism used with the arrangement shown in FIG. 14. In FIG. 15, the driving force transmitting mechanism includes a drive motor 13 comprised of a pulse motor, a motor gear 14 secured to a shaft of the drive motor, a convey roller gear 15 mounted on a shaft of the convey roller, idle gears 16, 17, and a sheet supply roller gear (clutch gear) 18 rotatably mounted on the sheet supply roller shaft 6. The motor gear 14 is meshed with the convey roller gear 15 which is in turn connected to the sheet supply roller gear 18 through the idle rollers 16, 17. Accordingly, when the motor gear 14 is rotated normally in a direction shown by the arrow a by normal rotation of the motor 13 (in the direction a), the convey roller gear 15 and the sheet supply roller gear 18 are also rotated normally. As a result, when a spring clutch 23 (described later) is in a clutch-on condition, the sheet supply roller 5 is rotated in a normal direction corresponding to a sheet feeding out direction (sub scan direction). Further, the convey roller 1 is also rotated in the normal direction corresponding to the sheet feeding out direction.
FIG. 16 is a side view of the spring clutch 23 provided on the sheet supply roller shaft 6, and FIG. 17 is a sectional view taken along the line 17--17 of FIG. 16. In FIG. 16, as mentioned above, the sheet supply roller gear 18 is rotatably mounted on the sheet supply roller shaft 6. A clutch drum 19 is fitted on the sheet supply roller shaft 6 in a confronting relation to the sheet supply roller gear 18 so that the clutch drum 19 cannot be rotated with respect to the shaft 6 by means of an idle rotation preventing pin 21. A cam portion 19A is integrally formed with the clutch drum 19. Stopper members 22, 24 serve to prevent the clutch drum 19 and the sheet supply roller gear 18 from shifting in a thrust direction. A coil-shaped clutch spring 25 is wound around a barrel 19B of the clutch drum 19 and a barrel 18B of the sheet supply roller gear 18. A control ring 20 surrounds the clutch spring 25.
An end of the clutch spring 25 near the clutch drum 19 is secured to the clutch drum 19, and the other end of the clutch spring is connected to the control ring 20. A lock lever 20A is integrally formed with the control ring 20. A stopper 26 is associated with the lock lever 20A and is driven by a solenoid (not shown).
In a clutch-off condition, the lock lever 20A of the control ring 20 is caught by the stopper 26 to prevent rotation of the control ring 20. As a result, the clutch spring 25 is loosen with respect to the barrel 18B of the sheet supply roller gear 18 to permit idle rotation of the sheet supply roller gear 18 on the shaft 6, with the result that the rotational force of the sheet supply roller gear 18 is not transmitted to the shaft 6. Accordingly, in this condition, even when the sheet supply roller gear 18 is being rotated, the sheet supply roller 5 is not rotated and is maintained in a stopped condition.
In the clutch-on condition, the stopper 26 is retarded from a movement path of the lock lever 20A of the control ring 20, thereby permitting the rotation of the control ring 20. As a result, the clutch spring 25 is tightened against the barrel 18B of the sheet supply roller gear 18, so that the sheet supply roller gear 18 is integrally connected to the clutch drum 19 via the clutch spring 25, with the result that the rotational force of the gear 18 is transmitted to the shaft 6 to rotate it together with the sheet supply roller gear 18, thereby rotating the sheet supply roller 5.
When a print signal is inputted to a control circuit (not shown) of the recording apparatus, the stopper 26 is retracted to release the spring clutch 23, thereby creating the clutch-on condition. Further, the motor 13 is rotated in the normal direction. As a result, the sheet supply roller 5 is rotated in the normal direction and the convey roller 1 is also rotated in the normal direction. Further, the downward biasing of the pressure plate 10 is released by rotation of the cam 19A, with the result that the pressure plate is lifted by the pressure plate spring 11 to urge a front end portion of the sheet stack 12 against a cylindrical peripheral portion of the sheet supply roller 5 which is now being rotated normally. Then, an uppermost sheet in the sheet stack 12 is picked up and conveyed by the further rotation of the sheet supply roller to be sent to the convey roller 1. If the other sheet(s) is picked up together with the uppermost sheet, the friction piece 8 serves to prevent the other sheet(s) from being sent to the convey roller.
In order to prevent the skew-feed of the sheet, after a tip end of the sheet supplied by the sheet supply roller 5 passes through a nip between the convey roller 1 and the pinch roller 2, when the sheet is conveyed in the sheet conveying direction by a predetermined amount in a condition that the sheet stack is urged against the sheet supply roller by means of the pressure plate, the motor 13 is rotated reversely. By doing so, since the clutch spring is loosen not to transmit the driving force to the sheet supply roller 5, the tip end of the sheet is returned to the nip between the convey roller 1 and the pinch roller 2 in a condition that a rear end portion of the sheet is held by the sheet supply roller 5. Then, the motor 13 is rotated normally again.
However, in the above-mentioned conventional technique, since the spring clutch is used to transmit the driving force to the sheet supply roller, the number of parts in the driving force transmitting mechanism is increased. Further, in order to ensure the reliability of the operation of the driving force transmitting mechanism, since the parts must be machined with higher accuracy, the driving force transmitting mechanism becomes expensive.
Further, since the spring clutch is used to prevent the skew-feed of the sheet, after the tip end of the sheet passes through the nip between the convey roller and the pinch roller, the sheet must be returned in the reverse direction and then be conveyed in the normal direction again. In this case, if the picked-up sheet is supplied greatly obliquely, a portion of the sheet will not be completely returned to the nip between the convey roller and the pinch roller during the reverse movement of the sheet, with the result that, even when the skew-feed preventing control is effected, the skew-feed of the sheet is not completely corrected. In order to solve this problem, an amount of the reverse movement of the sheet may be increased; in this case, however, a distance between the sheet supply roller and the convey roller must be increased, thus making the compactness of the apparatus difficult.